MFJ MFJ-836 User Manual
MFJ-836 SWR/Wattmeter and RF Ammeter Instruction Manual
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MFJ-836 SWR/Wattmeter and RF Ammeter
Introduction
The MFJ-836 is an all-in-one true peak reading SWR/Wattmeter with a built in RF
Ammeter designed to operate on 1.8-30 MHz. The SWR/Wattmeter uses our
TrueActive peak reading circuit to read true peak/average forward and reflected power
and SWR simultaneously. It has 3000/300 Watts forward and 600/60 Watts reflected
power scales. The SWR/Wattmeter utilizes a large illuminated three-inch Cross-Needle
meter to read the SWR from 1:1 to ∞. The RF Ammeter measures RF feedline current in
three calibrated ranges: 0.3 Amperes, 1 Ampere, and 3 Amperes.
Installation
1. Connect your transmitter to the connector on the back of the unit labeled
TRANSMITTER and your antenna to the connector labeled ANTENNA. It is
important that you use good quality coax and properly installed connectors.
2. The MFJ-836 has a TrueActive peak reading circuit included the
SWR/Wattmeter that requires a DC power supply such as the MFJ-1312B in order
to function. A 9 VDC may also be installed inside the meter with a battery clip
that is included. The rear panel accepts a 2.1 mm coaxial plug with the center
conductor positive (+) and the sleeve negative (-). The negative lead is grounded
inside the meter. There is no need to disconnect the battery when using external
power. The RF Ammeter does not require power to operate.
3. An internal lamp backlights the SWR/Wattmeter scale. The lamp circuit requires
12 VDC and will not illuminate with the 9 VDC battery alone.
4. To measure the power output capability of a transmitter/amplifier you should
connect a quality 50-ohm dummy load to the ANTENNA connector of the MFJ-
836.
NOTE:
The SWR/Wattmeter must have a power source in order to function. A nine-
volt battery may be installed in the compartment on the rear panel, or an
external 12 VDC source, such as the optional MFJ-1312D power supply, may
be used.
IMPORTANT:
Please read entire manual before attempting to operate this equipment. This
unit does not provide a dc or
low frequency earth ground. A separate wire
should be connected from the station ground bus to an electric ground. Do
not place any non-coaxial feed wires near metallic or RF sensitive devices.
MFJ-836 SWR/Wattmeter and RF Ammeter Instruction Manual
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Operation
1. With the DC power supply or 9 VDC battery installed, push the ON/OFF button
in to turn the unit ON. If 12 VDC is used, the SWR/Wattmeter backlight will also
be turned ON.
2. The SWR/Wattmeter’s full-scale forward and reflected power range is controlled
by the 3000/300-Watt button. When the button is pushed in, the forward power
scale is on 3000 Watts and the reflected power scale is on 600 Watts. When the
button is pushed out, the forward power scale is on 300 Watts and the reflected
power scale is on 60 Watts. If your transmitter/amplifier runs more than 300
Watts of output power, push the button in for 3000 Watts. If your transmitter runs
less than 300 Watts of output power, push the button out for 300 Watts.
3. Average power is measured when the PEAK/AVG button is pushed out. Peak
envelope power (PEP) is measured when the PEAK/AVG button is pushed in.
Peak and average power values are equal with steady unmodulated carriers, FSK,
or FM. The meter reading on these modes will be the same whether the
PEAK/AVG button is pushed in or out. On SSB, the PEP meter reading should
be twice the average power with two-tone test modulation. On SSB, the ratio of
PEP to average power varies with different voice characteristics. With most
voices, the PEP reading is three to five times higher than the average voice power
reading. The most accurate PEP readings are obtained only with sustained carrier,
voice or two-tone test modulation. During normal voice modulation, the
wattmeter will typically indicate only 70% of the true Peak Envelope Power.
4. Forward power is displayed on the left-hand FORWARD meter scale. This scale
is calibrated from 0 to 300 Watts and is read directly in the 300W (out) position.
Each picket (scale mark) represents 5 Watts below 10 Watts, 10 Watts between 10
and 100 Watts, and 25 Watts between 100 and 300 Watts. In the 3000W (in)
position, the forward power scale must be multiplied by 10. Each picket
represents 50 Watts below 100 Watts, 100 Watts from 100 to 1000 Watts, and 250
Watts from 1000 to 3000 Watts.
5. The reflected power is read on the right-hand REFLECTED meter scale.
Reflected power is 60-Watts full scale when the 300W (out) power scale is
selected, and 600-Watts full scale when the 3000W (in) power scale is selected.
6. The most accurate power readings occur in the upper half of the meter scales.
When trying to measure power with a less than perfect match, the reflected power
should be subtracted from the forward power reading in order to find the true
power.
7. The SWR is read directly from nine red SWR curves that range from 1:1 to ∞.
SWR is measured by observing the point where the forward and reflected power
MFJ-836 SWR/Wattmeter and RF Ammeter Instruction Manual
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needles cross. The SWR is indicated by the red curve closest to the needle
crossing point.
8. The RF Ammeter measures RF current in three calibrated ranges: 0.3 Amperes, 1
Ampere, and 3 Amperes. Simply turn the Current Range knob to the desired
range.
9. The meter is scaled from 0 to 100. On the 100-mA range, readout is direct (100 =
100 mA). On the 1-A range, move the decimal point 2 places to the left (100 =
1.00 A). To convert meter readings made on the 30 mA, 300 mA, and 3-A
ranges, multiply accordingly. For example, a reading of 85 on the 300-mA range
equals 300 x .85, or 255 mA. See Table 1 below to estimate readings quickly.
10. To prevent meter pegging, begin checks on a high range and work down. To
estimate unknown current levels, use the formula below (I = Unknown Current in
Amps, P = Applied Power in Watts, and R = Load Resistance in Ohms).
I
P
R
=
Range
Meter 300 mA 1 A 3 A
10 30 0.1 0.3
20 60 0.2 0.6
30 90 0.3 0.9
40 120 0.4 1.2
50 150 0.5 1.5
60 180 0.6 1.8
70 210 0.7 2.1
80 240 0.8 2.4
90 270 0.9 2.7
100 300 1.0 3.0
Table 1: Actual Current Value
RF Hazard--Important Warnings:
1. RF-current measurements must be conducted with extreme caution. Physical
contact with conductors carrying even moderate RF -energy levels can result in
severe RF burns, or injury.
2. Avoid measuring RF currents on conductors where high RF voltages may be
present (>500 Volts). Damage to your meter may result.
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